1. Field of the Invention
The present invention relates to image processing for a face image region.
2. Description of the Related Art
A technique for improving the image quality of a portrait is drawing increased attention. For example, a red eye correction technique disclosed in Japanese Patent Laid-Open No. 2002-247596, a technique which corrects a portrait to make skin look smooth is disclosed in Japanese Patent Laid-Open No. 11-250227, and the like are available.
In order to improve the impression of a portrait, the improvements of image qualities of not only eyes and skin but also the mouth have large influences. For example, correcting yellowed or stained teeth to be white makes these teeth look fresh and healthy, thus improving the impression of the entire portrait. Japanese Patent Laid-Open No. 2006-059162 discloses an invention which detects a tooth image region (to be referred to as a tooth image hereinafter) from a face image region (to be referred to as a face image hereinafter), and corrects the detected tooth image to be white according to a predetermined target value.
However, human perception is sensitive to the image quality of a face image. A balance is required between the colors of a given organ and another organ, and if the color of the given organ is largely different from that of another organ, one feels unnatural. For example, when a tooth image undergoes white correction, if the chroma level of the tooth image is too low with respect to that around the tooth image, only teeth in a face image stand out, resulting in an unnatural face image.
In particular, a face image generally having a high chroma level has a high chroma level of the color around teeth. If such tooth image undergoes white correction in the same manner as a face image generally having a low chroma level, a face image with teeth which stand out very much is formed. In other words, a target value required to correct the tooth image must be determined in consideration of the chroma level of the entire face image.